a = [1, 2, 3, 4, 5, 6, 7]
b = [8, 9, 10]
# 效率低
a += b
# 效率高
a.extend(b)

a = [1, 2, 3]
b = [4, 5, 6]
c = a + b
print(a)
print(b)
print(c)
print(c[:])

